In recent years, vehicles such as an electric vehicle (EV) and a hybrid electric vehicle (HEV) including an electric motor are increasing. For the purpose of improving the power efficiency of the EV and the HEV, an electric motor (motor) is used in high-speed rotation. Therefore, a bearing that is suitable for the high-speed rotation needs to be employed as a bearing for use with a motor main shaft.
Incidentally, as illustrated in FIG. 11, a related-art bearing (ball bearing) mainly includes an inner ring 2, an outer ring 3, a plurality of balls 4, and a retainer 5. The inner ring 2 has an inner raceway surface 2a formed in a radially outer surface of the inner ring 2. The outer ring 3 is arranged on an outer side of the inner ring 2 and has an outer raceway surface 3a formed in a radially inner surface of the outer ring 3. The plurality of balls 4 are interposed between the inner raceway surface 2a of the inner ring 2 and the outer raceway surface 3a of the outer ring 3 so as to be rollable. The retainer 5 made of resin is arranged between the inner ring 2 and the outer ring 3 and is configured to retain the balls 4 at equal intervals in a circumferential direction of the retainer 5. Any one of the outer ring 3 and the inner ring 2 is mounted to a stationary portion such as a housing, and another one of the outer ring 3 and the inner ring 2 is mounted to a rotary portion such as a rotary shaft.
As illustrated in FIG. 12A and FIG. 12B, the retainer 5 having a crown shape, which is arranged between the inner ring 2 and the outer ring 3, includes a main portion 5a and pairs of elastic pieces 5b. The main portion 5a has an annular shape. The pairs of elastic pieces 5b are integrally formed on one surface of the main portion 5a in an axial direction of the retainer 5 at equal intervals in the circumferential direction. The retainer 5 has pockets 5c, which are each formed so as to recess between each pair of elastic pieces 5b and are each opened on a radially outer side and a radially inner side of the retainer 5. The balls 4 are retained in the pockets 5c so as to be rollable.
Further, as illustrated in FIG. 11, on both sides of the inner ring 2 and the outer ring 3 in the axial direction, there are arranged sealing members 6 configured to seal an annular space formed between the inner ring 2 and the outer ring 3. Each sealing member 6 includes a core 6a and an elastic member 6b. The elastic member 6b integrally adheres to the core 6a through vulcanization. A base end portion of each sealing member 6 is mounted to a radially inner end portion of the outer ring 3, and a distal end portion of each sealing member 6 has a seal lip 6c held in contact with a radially outer end portion of the inner ring 2. In the ball bearing 1 illustrated in FIG. 11, the outer ring 3 to which the base end portions of the sealing members 6 are mounted is on a stationary side, and the inner ring 2 with which the seal lips 6c are held in contact is on a rotary side.
During operation of the ball bearing 1, the inner ring 2 is rotated while maintaining a state in which the seal lips 6c formed at the distal ends of the sealing members 6 are held in slide contact with the radially outer end portion of the inner ring 2. With this action, entry of foreign matters such as water and dust into the bearing or leakage of a lubricant such as grease from an inside of the bearing to an outside is prevented.
When such a bearing is used in high-speed rotation, the retainer made of resin may be deformed by a centrifugal force and generate abrasion powder through interference with other components. As a result, abnormal heat generation is concerned, and there is a fear in that lifetime is shortened. Therefore, there have hitherto been proposed various solutions for the above-mentioned problem using the centrifugal force generated at the time of high-speed rotation (Patent Literature 1 to Patent Literature 4).
According to a retainer disclosed in Patent Literature 1, the retainer includes an annular portion and a plurality of cantilevered columnar portions extending from one side surface of the annular portion. Balls are received in pockets, which are each formed between the annular portion and adjacent columnar portions, so as to be rollable. In consideration of radial deformation caused by a centrifugal force, the retainer has the structure of being inclined radially inward from the annular portion toward the distal end portions of the columnar portions by a predetermined amount of deformation caused by the centrifugal force in advance. With this structure, when deformation caused by the centrifugal force occurs during high-speed rotation, the inclination is corrected, and the columnar portions are brought into a substantially horizontal state in the axial direction, thereby achieving suitable contact positions of the balls with respect to the pockets of the retainer.
According to a retainer disclosed in Patent Literature 2, in a combination retainer made of synthetic resin, when hook portions being engaging portions of a second element and step portions being engaged portions of a first element are engaged with each other, elastic deformation of the engaging portions is reduced or eliminated. Further, under the state in which both elements are engaged with each other, fixing pieces for filling gaps with protruding portions are inserted to through holes, and both the elements are integrally fixed to each other by the fixing pieces, thereby enhancing engagement between both the elements.
According to Patent Literature 3, as illustrated in FIG. 1 of Patent Literature 3, recessed portions (thinned portions) are formed in a radially inner portion of a crown-shaped retainer, thereby preventing abutment against a portion of each ball with high rotation speed during high-speed rotation. That is, the portion of interference between an inner wall surface, which constructs pockets of the crown-shaped retainer, and each ball.
According to Patent Literature 4, a support ring, which is formed of an annular metal plate having a rigidity higher than that of synthetic resin of a crown-shaped retainer for a ball bearing, is integrally fixed to the crown-shaped retainer through adhesion or the like. With this configuration, the rigidity of the retainer is enhanced. Further, according to a retainer for a bearing disclosed in Patent Literature 5, the retainer includes a retainer main body, which is made of synthetic resin, and a deformation preventing member, which is made of metal and is connected to the retainer main body. Therefore, the retainer for a bearing disclosed in Patent Literature 5 enhances the rigidity of the retainer, similarly to the crown-shaped retainer for a ball bearing disclosed in Patent Literature 4. Further, there has hitherto been proposed a retainer which is reduced in inner diameter to decrease the weight so that the centrifugal force is controlled.